Pro-fragrances and method of preparation thereof

ABSTRACT

is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national stage entry according to 35 U.S.C.§ 371 of PCT application No.: PCT/EP2018/075923 filed on Sep. 25, 2018;which claims priority to German Patent Application Serial No.: 10 2017122 983.3, which was filed on Oct. 4, 2017; which is incorporated hereinby reference in its entirety and for all purposes.

TECHNICAL FIELD

Compounds based on 1-Aza-3,7-dioxabicyclo[3.3.0]octane (bicyclicoxazolidine derivative) may be substituted with3-(4-isobutyl-2-methylphenyl)propyl, and more particularly may be usedin pro-fragrance compositions.

BACKGROUND

In addition to the use of fragrances in detergent, cleaning, fabricsoftening and cosmetic composition, it is also known to usepro-fragrances in such compositions. By analogy with pro-drugs,pro-fragrances are chemical derivatives of a fragrance, which forexample reduce the volatility of the fragrance and allow a delayedrelease of the fragrance over time under ambient conditions. Byderivatization of fragrances, such as aldehyde or ketone fragrances, thevapor pressure of these compounds can be lowered. Since thederivatization reaction is reversible, the chemically bound aldehyde orketone fragrance may, under certain conditions, e.g., ambientconditions, be released, which may lead to a prolonged scent impression.

The base compound used for forming the pro-fragrance is a1-aza-3,7-dioxabicyclo[3.3.0]octane (bicyclic oxazolidine derivative).Such oil-soluble substituted monocyclic and bicyclic oxazolidines aredisclosed for the use as additives in automatic transmission fluids, forexample, in U.S. Pat. No. 4,277,353. Examples described therein includereaction products of optionally substituted 2-amino-1,3-propanediolswith paraformaldehyde and isobutyraldehyde.

Pro-fragrance compounds based on 1-aza-3,7-dioxabicyclo[3.3.0]octanederivatives are for example disclosed in WO 2007/087977 A1. In thisreference a generic formula for those compounds is disclosed togetherwith a long list of exemplary compounds for aldehydes or ketones thatare commonly used as fragrances.

An object of the present invention was to identify further oxazolidinecompounds of the general formula of WO 2007/087977 A1, that provide fora prolonged scent perception, in particular in comparison to theexplicitly disclosed examples of this reference.

SUMMARY

The present inventors have surprisingly found that1-aza-3,7-dioxabicyclo[3.3.0]octane (bicyclic oxazolidine derivatives)compounds substituted with 3-(4-isobutyl-2-methylphenyl)propyl, producedby reacting the corresponding aldehyde3-(4-isobutyl-2-methylphenyl)propanal (commercially available under thetradename nympheal) with serinol or a derivative thereof, provide forimproved scent long-lastingness and intensity compared to other known1-aza-3,7-dioxabicyclo[3.3.0]octane compounds, for example thosesubstituted with 3-(4-tert-butylphenyl)-2-methylpropyl (using thecorresponding aldehyde 3-(4-tert-butylphenyl)-2-methylpropanal(lilial)).

In a first aspect, a compound based on1-aza-3,7-dioxabicyclo[3.3.0]octane may be substituted with3-(4-isobutyl-2-methylphenyl)propyl represented by formula (I)

wherein

R^(a) is hydrogen or a C₁₋₂₀ alkyl group which can optionally besubstituted with hydroxyl groups and/or amine groups and/or in which upto 8 —CH₂— groups which are not adjacent to each other can besubstituted by —O—, such as R^(a) is hydrogen or C₁₋₆ alkyl,alternatively R^(a) is hydrogen or methyl, or R^(a) is hydrogen;

R^(b) and R^(c) are independently selected from hydrogen or C₁₋₆ alkyl,such as R^(b) and R^(c) are independently selected from hydrogen andmethyl, alternatively R^(b) and R^(c) are both hydrogen.

In a second aspect, a mixture of at least one compound of formula (I) asdescribed above may be mixed with at least one compound of formula (II)

wherein

R^(a) is hydrogen or a C₁₋₂₀ alkyl group which can optionally besubstituted with hydroxyl groups and/or amine groups and/or in which upto 8 —CH₂— groups which are not adjacent to each other can besubstituted by —O—, such as R^(a) is hydrogen or C₁₋₆ alkyl,alternatively R^(a) is hydrogen or methyl, or R^(a) is hydrogen;

R^(b) and R^(c) are independently selected from hydrogen or C₁₋₆ alkyl,such as R^(b) and R^(c) are independently selected from hydrogen andmethyl, alternatively R^(b) and R^(c) are both hydrogen.

DETAILED DESCRIPTION

The inventive compounds of formulae (I) and (II) are useful aspro-fragrances, as the bound aldehyde is released over time and providesfor the desired scent experience.

“One or more”, as used herein, relates to at least one and comprises 1,2, 3, 4, 5, 6, 7, 8, 9 or more of the referenced species. Similarly, “atleast one” means one or more, i.e. 1, 2, 3, 4, 5, 6, 7, 8, 9 or more.“At least one”, as used herein in relation to any component, refers tothe number of chemically different molecules, i.e. to the number ofdifferent types of the referenced species, but not to the total numberof molecules. For example, “at least one aldehyde” means that at leastone type of molecule falling within the definition for an aldehyde isused but that also two or more different molecule types falling withinthis definition can be present, but does not mean that only one moleculeof said aldehyde is present.

If reference is made herein to a molecular weight, this reference refersto the weight average molecular weight M_(w), if not explicitly statedotherwise. The weight average molecular weight can be determined by gelpermeation chromatography.

All percentages given herein in relation to the compositions orformulations relate to weight % relative to the total weight of therespective composition or formula, if not explicitly stated otherwise.

It has been surprisingly found by the inventors that compounds based on1-aza-3,7-dioxabicyclo[3.3.0]octane substituted with3-(4-isobutyl-2-methylphenyl)propyl have an improved prolonged scentimpression compared to the compounds of this type known in the priorart. Furthermore, it has been found that the deposition of such bicycliccompounds on solid surfaces such as textiles, skin or hard surfaces isimproved.

The compounds of formulae (I) and (II) can be obtained by a method thatcomprises reacting at least one compound of formula (III)

wherein

R^(a) is hydrogen or a C₁₋₂₀ alkyl group which can optionally besubstituted with hydroxyl groups and/or amine groups and/or in which upto 8 —CH₂— groups which are not adjacent to each other can besubstituted by —O—, such as R^(a) is hydrogen or C₁₋₆ alkyl,alternatively R^(a) is hydrogen or methyl, or R^(a) is hydrogen;

R^(b) and R^(c) are independently selected from hydrogen or C₁₋₆ alkyl,such as R^(b) and R^(c) are independently selected from hydrogen andmethyl, alternatively R^(b) and R^(c) are both hydrogen; with

a compound of formula

in a ring forming reaction. In this reaction the aldehyde group of3-(4-isobutyl-2-methylphenyl)propanal reacts with the hydroxyl and theamino groups of the compound of formula (III) to form the compounds offormula (I) and/or (II).

The compounds of general formula (III) are derived from2-amino-1,3-propanediol (serinol). By producing the bicyclic compounds,it is possible to achieve a high degree of loading of the2-amino-1,3-propanediols, so that the use of smaller amounts of2-amino-1,3-propanediols is possible. This achieves a prolongation ofthe scent impression even with smaller amounts of2-amino-1,3-propanediols, which can lead to cost advantages and alsoavoids the introduction of large quantities of chemicals into detergent,cleaning, fabric softening or cosmetic compositions.

As can be seen from the above, it is also possible to use monocycliccompounds based on 2-amino-1,3-propanediols, i.e. the compounds offormula (II). These are generated as byproducts in the synthesis of thecompounds of formula (I). It is possible to achieve a high degree ofloading of the 2-amino-1,3-propanediols, so that bicyclic oxazolidinesare generally used.

In compounds according to formula (I) R^(a) is hydrogen or a C₁₋₂₀ alkylgroup which can optionally be substituted with hydroxyl groups and/oramine groups and/or in which up to 8 —CH₂— groups which are not adjacentto each other can be substituted by —O—, such as R^(a) is hydrogen orC₁₋₆ alkyl, alternatively R^(a) is hydrogen or methyl, or R^(a) ishydrogen;

R^(b) and R^(c) are independently selected from hydrogen or C₁₋₆ alkyl,such as R^(b) and R^(c) are independently selected from hydrogen andmethyl, alternatively R^(b) and R^(c) are both hydrogen.

In various embodiments, R^(a) is hydrogen or methyl and R^(b) and R^(c)are hydrogen. Non-limiting embodiments may include R^(a) is methyl andR^(b) and R^(c) are hydrogen. Alternatively, R^(a) to R^(c) are allhydrogen. This provides for an improved long-lastingness of the scentand high intensity even after prolonged periods of time.

To produce the compounds of formula (I) the amino alcohol of formula(III) is reacted with an aldehyde of formula (IV) which is3-(4-isobutyl-2-methylphenyl)propanal, commercially available under thename nympheal and having the CAS No. 1637294-12-2. According to oneembodiment, the compounds of general formula (I) are derived from a2-amino-1,3-propanediol molecule of formula (III) and two aldehydemolecules of formula (IV). In the reaction of less than stoichiometricamounts of aldehydes, monocyclic compounds are also present in theproduct mixture. The amount of bicyclic compounds to monocycliccompounds may be adjusted easily through the choice of the molar ratiosbetween aldehyde and 2-amino-1,3-propanediol. Large amounts of bicyclicstructures are especially useful. Such mixtures contain at least 50wt.-%, such as at least 65 wt.-%, or at least 80 wt.-% of bicyclicstructures, based on the total weight of the compounds. In variousembodiments, this means that in the mixtures of compounds according toformulae (I) and (II), the amount of compounds of formula (I) is higherthan 50 mol.-% relative to the total amount of compounds of formulae (I)and (II), such as higher than 70 mol.-%, alternatively higher than 80mol.-%, or at least 90 mol.-%.

The reaction is performed in a suitable solvent or in situ, such as in asuitable solvent. Suitable solvents include, for example, hydrocarbonscontaining aromatics, in particular toluene. The reaction is carried outat a temperature in the range of 80 to 150° C., such as 100 to 140° C.,alternatively at 120° C. For example, as the starting material thecompound of general formula (III) is used together with the aldehyde andthe solvent under nitrogen atmosphere. This reaction mixture is thenheated, such as from 5 minutes to 20 hours, alternatively from 1 to 10hours, or from 6 to 8 hours, whereupon the solids gradually go intosolution. The reaction is finished when no more water as by-product ofthe reaction is produced. The mixture is heated under reflux on a waterseparator. The resulting reaction product is isolated by conventionalmethods, for example by drying in vacuum, and purified if necessary.

The compounds are used as pro-fragrances. The term “pro-fragrance”describes in general derivatives of aldehyde and ketone fragrances,which release the original aldehydes and ketones under ambientconditions. Ambient conditions are typical ambient conditions in thehuman biosphere and/or the conditions encountered on human skin. Thecompounds of general formula (I) and (II) disintegrate slowly underambient conditions in a reversal of the synthesis process, releasing theoriginal aldehydes. Accordingly, the compounds may be used aspro-fragrances.

The at least one compound may be used as the only fragrance substance,but it is also possible to use mixtures of fragrances, which arecomprised only partially of the at least one compound. In particular,fragrance mixtures containing 1 to 50 wt.-%, such as 5 to 40.-wt.-%, andin particular max. 30 wt.-% of the at least one compound of formula (I)or the mixture of compounds of formulae (I) and (II), based on the totalweight of the fragrance mixture may be used. In a non-limitingembodiment, the at least one compound or compound mixture can be usedtogether with further fragrance compounds different from the compoundsof formulae (I) and (II). By the use of additional perfume compounds inthe compositions, e.g., detergent or cleaning compositions, it ispossible to create a variety of characteristics of the final product,which are only possible by using them in combination with the at leastone compound or the mixture of the compounds. For example, it ispossible to divide the total perfume content (fragrance content) of acomposition, for example a detergent or cleaning composition, into twoportions, x and y, wherein portion x comprises the compounds and portiony comprises traditional scent substances, like perfume oils.

The fragrance substances (or perfume compounds, with these two termsbeing used interchangeably herein) that may be additionally incorporatedare not subject to any restrictions. Individual perfume substancecompounds of natural or synthetic origin, e.g., of the type of esters,ethers, aldehydes, ketones, alcohols and hydrocarbons may thus be usedas the perfume substance including perfume oils. Fragrance compounds ofthe ester type include, for example, benzyl acetate, phenoxyethylisobutyrate, p-tert-butylcyclohexyl acetate, linalyl acetate,dimethylbenzylcarbinyl acetate (DMBCA), phenylethyl acetate, benzylacetate, ethylmethyl phenyl glycinate, allylcyclohexyl propionate,styrallyl propionate, benzyl salicylate, cyclohexylsalicylate, floramat,melusat and jasmacyclate. The ethers include, for example, benzylethylether and ambroxan; the aldehydes include, for example, the linearalkanals with 8 to 18 carbon atoms, citral, citronellal, citronellyloxyacetaldehyde, cyclamenaldehyde, lilial and bourgeonal; the ketonesinclude, for example, the ionones, α-isomethylionone and methyl cedrylketone; the alcohols include anethole, citronellol, eugenol, geraniol,linalool, phenylethyl alcohol and terpineol; the hydrocarbons includemainly terpenes such as limonene and pinene. However, mixtures ofvarious fragrance substances which jointly produce an attractive scentnote may be used.

Such fragrance substances may also contain mixtures of natural perfumesubstances such as those accessible from plant sources, e.g., pine oil,citrus oil, jasmine oil, patchouli oil, rose oil or ylang-ylang oil.Also suitable are muscatel sage oil, chamomile oil, clove oil, lemonbalm oil, mint oil, cinnamon leaf oil, linden blossom oil, juniper berryoil, vetiver oil, olibanum oil, galbanum oil and labdanum oil as well asorange blossom oil, neroli oil, orange peel oil and sandalwood oil.

Other traditional fragrance substances that may be used within the scopeinclude, for example, the essential oils such as angelica root oil,anise oil, arnica blossom oil, sweet basil oil, bay oil, champacablossom oil, silver fir oil, fir cone oil, elemi oil, eucalyptus oil,fennel oil, spruce needle oil, galbanum oil, geranium oil, ginger grassoil, guaiac wood oil, gurjun balsam oil, helichrysum oil, ho oil, gingeroil, iris oil, cajeput oil, calamus oil, chamomile oil, camphor oil,canaga oil, cardamom oil, cassia oil, pine needle oil, copaiba balsamoil, coriander oil, spearmint oil, caraway oil, cumin oil, lavender oil,lemon grass oil, lime oil, mandarin oil, lemon balm oil, ambrette seedoil, myrrh oil, clove oil, neroli oil, niaouli oil, olibanum oil,origanum oil, palmarosa oil, patchouli oil, Peru balsam oil, petitgrainoil, pepper oil, peppermint oil, allspice oil, pine oil, rose oil,rosemary oil, sandalwood oil, celery seed oil, spike lavender oil, staranise oil, turpentine oil, thuja oil, thyme oil, verbena oil, vetiveroil, juniper berry oil, vermouth oil, wintergreen oil, ylang-ylang oil,ysop oil, cinnamon oil, cinnamon leaf oil, citronella oil, lemon oil andcypress oil as well as compounds selected from the group ofambrettolide, ambroxan, α-amylcinnamaldehyde, anethole, anise aldehyde,anise alcohol, anisole, anthranilic acid methyl ester, acetophenone,benzylacetone, benzaldehyde, benzoic acid ethyl ester, benzophenone,benzyl alcohol, benzyl acetate, benzyl benzoate, benzyl formate, benzylvalerate, borneol, bornyl acetate, boisambrene forte, α-bromostyrene,n-decylaldehyde, n-dodecylaldehyde, eugenol, eugenol methyl ether,eucalyptol, farnesol, fenchone, fenchyl acetate, geranyl acetate,geranyl formate, heliotropin, heptin carboxylic acid methyl ester,heptaldehyde, hydroquinone dimethyl ester, hydroxycinnamyl aldehyde,hydroxycinnamyl alcohol, indole, iron, isoeugenol, isoeugenol methylether, isosafrol, jasmine, camphor, carvacrol, carbon, p-cresol methylether, coumarin, p-methoxyacetophenone, methyl-n-amyl ketone, methylanthranilic acid methyl ester, p-methylacetophenone, methyl chavicol,p-methylquinoline, methyl β-naphthyl ketone, methyl n-nonylaldehyde,nonyl alcohol, n-octylaldehyde, p-oxyacetphenone, pentadecanolide,β-phenylethyl alcohol, phenylacetaldehyde-dimethylacetal, phenylaceticacid, pulegon, safrole, salicylic acid isoamyl ester, salicylic acidmethyl ester, salicylic acid hexyl ester, salicylic acid cyclohexylester, santalol, sandelice, skatol, terpineol, thyme, thymol, troenan,γ-undelactone, vanillin, veratrum aldehyde, cinnamyl aldehyde, cinnamylalcohol, cinnamic acid, cinnamic acid ethyl ester, cinnamic acid benzylester, diphenyl oxide, limonene, linalool, linayl acetate and linalylpropionate, melusat, menthol, menthone, methyl-n-heptenone, pinene,phenyl acetaldehyde, terpinyl acetate, citral, citronellal and mixturesthereof.

All fragrance substances disclosed herein, can be used in thecompositions or agents in free or encapsulated form or both.Specifically, the compounds of formulae (I) and (II) can be used in freeor encapsulated form or both. As they are used as precursors, they areused in free, i.e. non-encapsulated form. In various embodiments, theycan be combined with encapsulated fragrances, wherein these may alsoinclude free nympheal. As capsules, microcapsules can be used, all ofwhich are known in the art and include, without limitation, aminoplastand acrylate microcapsules. The microcapsules in which the fragrances orpro-fragrances are encapsulated may have a core-shell morphology, withthe shell being typically formed of a polymer, or alternatively may havethe form of matrix particles in which the fragrance substances areentrapped.

The at least one compound of formula (I) or the mixture of compounds offormulae (I) and (II) can be used in perfume compositions, can bepresent in those in amounts of 0.001 to 100 wt.-% relative to the totalweight of the perfume composition, such as in amounts of 0.1 to 90wt.-%, such as 1 to 90 wt.-%, 2 to 85 wt.-%, 5 to 75 wt.-% or 10 to 50wt.-%.

EXAMPLES Synthesis of 1-aza-3,7-dioxabicyclo[3.3.0]octanes AA1: GeneralOperating Procedure for Synthesis of1-aza-3,7-dioxabicyclo[3.3.0]octanes, amino Alcohol/Aldehyde Ratio 1:2

The amino alcohol and the aldehyde were combined in a 1:2 molar ratio intoluene as the solvent under nitrogen atmosphere. The reaction mixturewas heated to 120° C., whereupon the amino alcohol slowly goes intosolution. The mixture was refluxed using a water separator for 7 hours.The resulting product was obtained by removing the solvent by rotatingvacuum distillation and drying in high vacuum.

AA2: General Operating Procedure for Synthesis of1-aza-3,7-dioxabicyclo[3.3.0]octanes, amino alcohol/aldehyde Ratio 1:2In Situ

The amino alcohol was combined with the aldehyde in a 1:2 molar ratiounder nitrogen atmosphere. The reaction mixture was heated to 100-140°C., whereupon the reactants go into solution slowly or melt. Thereaction mixture is heated until no more reaction water can be distilledoff. The transparent slightly yellowish solution was dried in a highvacuum.

Example 1: Synthesis of2,8-bis[2-[2-methyl-4-(2-methylpropyl)phenyl]ethyl]-3.7-dioxa-1-azabicyclo[3.3.0]octane

According to the general procedure AA2 22.75 g 2-amino-1,3-propandiol(CAS 534-03-2) and 103.02 g 3-(4-isobutyltolyl)propionaldehyde(Nympheal) (CAS 1637294-12-2) were heated to 120° C. during 5 hours toafford 115.65 g (100%) of the desired compound as a yellow oil.

R_(f) (1% v/v Et₃N in Et₂O/nHex 1:1)=0.52. GC (45° C.—0 min; 300° C.—14min; 15° C./min): 20.2 min, 21.1 min. ¹H NMR (400 MHz, CDCl₃) −δ (ppm)7.10-7.00 (m, 2H), 6.95-6.85 (m, 4H), 4.50 (t, J=5.5 Hz, 2H), 4.12 (dd,J=8.5 Hz, 6.5 Hz, 2H), 3.87 (m, 1H), 3.68 (dd, J=8.5 Hz, 4.7 Hz, 2H),2.75-2.62 (m, 4H), 2.40 (m, 4H), 2.29 (s, 6H), 1.91-1.72 (m, 6H),0.98-0.72 (m, 12H)¹³C NMR (101 MHz, CDCl₃) −δ (ppm) 139.3 (s, 2C), 137.0(s, 2C), 136.6 (s, 2C), 131.1 (d, 2C), 128.4 (d, 2C), 126.7 (d, 2C),96.7 (d, 1C), 69.7 (t, 2C), 62.3 (d, 2C), 45.0 (t, 2C), 35.8 (t, 2C),30.2 (d, 2C), 28.2 (t, 2C), 22.4 (q, 4C), 19.3 (q, 2C). MS (ESI+): 464[M+H]⁺ (100%).

Comparative Example 1

Instead of 3-(4-isobutyltolyl)propionaldehyde the aldehyde lilial wasused. The synthesis was carried out as described for the inventiveexample above.

Olfactory Test

The aldehydes nympheal and lilial in free form as well as the compoundof Example 1 and Comparative Example 1 were tested for their performanceas follows. The afore-mentioned compounds were mixed into a standardsolid powder detergent (65 g dose (Persil)) so that the initial scentintensity of the free compounds nympheal and lilial on the one hand andthe scent intensity of the respective oxazolidine precursors was aboutthe same. The scent intensity was evaluated by four trained perfumers ona scale of 0 to 5, where 5 is the highest score and 0 stands for noperception of scent. The scent was evaluated on textiles after washing3.5 kg laundry in a standard washing machine (standard program at 40°C.). Three different types of laundry were used, namely blended fabric,cotton and polyester. The scent was evaluated on the laundry being inwet state directly after washing, in dry state immediately after thelaundry had dried and 7 days after the washing/drying. The assessmentwas performed 5 times, respectively and the results are displayed asaverage values. The results are displayed in Table 1 below.

Definition of the Scale

5 very strong

4 strong

3 pleasant

2 perceptible

1 not perceptible

TABLE 1 Results of the olfactory test. After 7 After 7 After 7 Wet WetWet Dry Dry Dry days days days Compound (1) (2) (3) (1) (2) (3) (1) (2)(3) Example 1 3.80 3.70 4.38 3.60 3.70 3.80 3.33 4.33 3.83 Nympheal 2.402.10 2.50 2.30 2.30 2.30 2.5 3.00 3.00 Comparative 2.13 2.38 2.38 2.002.50 2.50 2.75 3.25 3.00 Example 1 Lilial 2.13 2.50 2.25 2.00 2.75 2.252.75 3.00 3.00 (1) = blended fabric, (2) = cotton, (3) = polyester Scentimpression of the dosing units before washing Nympheal = 3.3; Example 1= 2.38; Lilial = 3.4; Comparative Example 1 = 2.2.

As can be seen by the results shown in Table 1, the compounds of example1 show an improved long-lasting scent impression compared to thecompounds of comparative example 1.

1. A compound based on 1-Aza-3,7-dioxabicyclo[3.3.0]octane substitutedwith 3-(4-isobutyl-2-methylphenyl)propyl represented by formula (I):

wherein: R^(a) is hydrogen, a C₁₋₂₀ alkyl, or combinations thereof; theC₁₋₂₀ alkyl is optionally substituted with hydroxyl groups, aminegroups, or combinations thereof; up to 8 —CH₂— groups of the C₁₋₂₀ alkylare substituted by —O— groups; and the up to 8 —CH₂— groups are notadjacent to each other; and R^(b) and R^(c) are independently selectedfrom hydrogen, C₁₋₆ alkyl, or combinations thereof.
 2. A compositioncomprising at least one compound of formula (I) according to claim 1 andat least one compound of formula (II)

wherein: R^(a) is hydrogen, a C₁₋₂₀ alkyl, or combinations thereof; theC₁₋₂₀ alkyl is optionally substituted with hydroxyl groups, aminegroups, or combinations thereof; up to 8 —CH₂— groups of the C₁₋₂₀ alkylare substituted by —O— groups; and the up to 8 —CH₂— groups are notadjacent to each other; and R^(b) and R^(c) are independently selectedfrom hydrogen, C₁₋₆ alkyl, or combinations thereof.
 3. A method forpreparing a compound according to claim 1 by reacting at least onecompound of formula (III)

wherein: R^(a) is hydrogen, a C₁₋₂₀ alkyl, or combinations thereof; theC₁₋₂₀ alkyl is optionally substituted with hydroxyl groups, aminegroups, or combinations thereof; up to 8 —CH₂— groups of the C₁₋₂₀ alkylare substituted by —O— groups; and the up to 8 —CH₂— groups are notadjacent to each other; and R^(b) and R^(c) are independently selectedfrom hydrogen, C₁₋₆ alkyl, or combinations thereof; with a compound offormula

in a ring forming reaction.
 4. (canceled)
 5. (canceled)
 6. (canceled) 7.A pro-fragrance composition comprising the compound of formula (I)according to claim
 1. 8. The pro-fragrance composition of claim 7,wherein the compound releases the fragrance compound of formula (IV):


9. The pro-fragrance composition of claim 7, further comprising one ormore additional fragrance compounds different from that of the compoundof formula (I).
 10. The pro-fragrance composition of claim 7, whereinR^(a) of the compound of formula (I) is a C₁₋₆ alkyl.
 11. Thepro-fragrance composition of claim 7, wherein R^(a) of the compound offormula (I) is methyl.
 12. The pro-fragrance composition of claim 7,wherein R^(a) of the compound of formula (I) is hydrogen.
 13. Thepro-fragrance composition of claim 7, wherein R^(b) and R^(c) of thecompound of formula (I) are independently selected from hydrogen,methyl, or combinations thereof.
 14. The pro-fragrance composition ofclaim 7, wherein R^(b) and R^(c) of the compound of formula (I) are bothhydrogen.
 15. The pro-fragrance composition of claim 7, furthercomprising at least one compound of formula (II):

wherein: R^(a) is hydrogen, a C₁₋₂₀ alkyl, or combinations thereof; theC₁₋₂₀ alkyl is optionally substituted with hydroxyl groups, aminegroups, or combinations thereof; up to 8 —CH₂— groups of the C₁₋₂₀ alkylare substituted by —O— groups; and the up to 8 —CH₂— groups are notadjacent to each other; and R^(b) and R^(c) are independently selectedfrom hydrogen, C₁₋₆ alkyl, or combinations thereof.
 16. Thepro-fragrance composition of claim 15, wherein R^(a) of the compound offormula (II) is a C₁₋₆ alkyl.
 17. The pro-fragrance composition of claim15, wherein R^(a) of the compound of formula (II) is methyl.
 18. Thepro-fragrance composition of claim 15, wherein R^(a) of the compound offormula (II) is hydrogen.
 19. The pro-fragrance composition of claim 15,wherein R^(b) and R^(c) of the compound of formula (II) areindependently selected from hydrogen, methyl, or combinations thereof.20. The pro-fragrance composition of claim 15, wherein R^(b) and R^(c)of the compound of formula (II) are both hydrogen.